We endeavored to identify objective blood biomarkers for pain, a subjective sensation with a biological basis, using a stepwise discovery, prioritization, validation, and testing in independent cohorts design. We studied psychiatric patients, a high risk group for co-morbid pain disorders and increased perception of pain. For discovery, we used a powerful within-subject longitudinal design. We were successful in identifying blood gene expression biomarkers that were predictive of pain state, and of future emergency department (ED) visits for pain, more so when personalized by gender and diagnosis. MFAP3, which had no prior evidence in the literature for involvement in pain, had the most robust empirical evidence from our discovery and validation steps, and was a strong predictor for pain in the independent cohorts, particularly in females and males with PTSD. Other biomarkers with best overall convergent functional evidence for involvement in pain were GNG7, CNTN1, LY9, CCDC144B, and GBP1. Some of the individual biomarkers identified are targets of existing drugs. Moreover, the biomarker gene expression signatures were used for bioinformatic drug repurposing analyses, yielding leads for possible new drug candidates such as SC-560 (an NSAID), and amoxapine (an antidepressant), as well as natural compounds such as pyridoxine (vitamin B6), cyanocobalamin (vitamin B12), and apigenin (a plant flavonoid). Our work may help mitigate the diagnostic and treatment dilemmas that have contributed to the current opioid epidemic.

Amoxapine is marketed as an antidepressant. However, its in-vitro profile, receptor occupancy and preclinical effects are very similar to atypical antipsychotics. Amoxapine has also shown efficacy as an atypical antipsychotic in open trials. The objective of this study was to compare the antipsychotic and side effect profile of amoxapine and risperidone in a randomised assignment, standardized dosing, double-blind trial of acutely psychotic patients with schizophrenia. A total of 48 schizophrenic patients were enrolled and randomized in a double-blind 6-week trial to receive either risperidone (up to 5 mg/day) or amoxapine (up to 250 mg/day). Positive, negative, affective symptoms and motor side effects were measured using standardized weekly assessments. Prolactin levels were also determined at baseline and at the end of the study. A total of 39 patients (amoxapine, n=22; risperidone, n=21) completed the trial. Both pharmacological treatments, amoxapine 228.0 mg/day (SD=34.6) and risperidone 4.5 mg/day (SD=0.7), showed equivalent improvement in positive, negative, and depressive symptoms. Amoxapine was associated with less EPS and less prolactin elevation than risperidone. These data support previous reports about the efficacy of amoxapine as an atypical antipsychotic. Since amoxapine is off-patent, it may be a valuable low-cost alternative to new atypical antipsychotics, particularly in low-income countries where the majority of the patients are still treated with typical antipsychotics.

Antidepressant drugs are extensively metabolized prior to elimination from the body. These metabolites usually have biological and chemical properties different from those of the parent drug. This article explores the pharmacodynamic consequences of such metabolism as possibly contributing to failure to respond to or tolerate a drug. Differential side effects, especially of tricyclic antidepressant metabolites, are considered. Next, shifts in effects of presumed serotonin uptake inhibitors are described. Problems involving active metabolites of more novel compounds such as bupropion, amoxapine and trazodone range from possible reversal of response to prohibitive side effects. Finally, principles are deduced for identifying those cases in which metabolic considerations are most likely to be relevant to observed drug resistance.

Cognitive effects of brief antidepressant treatments were studied in depressed outpatients assigned double-blind to equipotent doses of amoxapine or amitriptyline in a 12-week double-crossover of 3-week periods of active agent and placebo. The two drugs had different profiles of effects: amitriptyline was associated with faster reaction time on tests of attention and immediate memory, reduced accuracy on an attention task, and impaired long-term memory (after 1 but not 3 weeks); amoxapine slowed performance and increased intraperson variability on a psychomotor coordination task. Amitriptyline facilitated performance in the more depressed patients, and amoxapine in the older patients. Both agents also increased pulse rate and reduced palmar sweating.

This study was designed to evaluate the antidepressant activity of various antidepressants using the learned helplessness test (LH) or the forced swimming test (FS) in rats. Repeated treatment of the tricyclic antidepressants imipramine (10 mg/kg, p.o.), clomipramine (0.625 mg/kg, p.o.), amitriptyline (10 mg/kg, p.o.) and amoxapine (20 mg/kg, p.o.) reduced the number of escape failures in the LH group, respectively. Repeated treatment of an atypical antidepressant, mianserin (2.5 and 5 mg/kg, p.o.), and one of the selective serotonin reuptake inhibitors (SSRI), fluvoxamine (1.25 mg/kg, p.o.), also reduced the number of escape failures in the LH group. In the FS, repeated treatment of imipramine (5, 10 mg/kg, p.o.), amitriptyline (5, 10 mg/kg, p.o.) and mianserin (10 mg/kg) significantly decreased the duration of immobility time. On the other hand, repeated treatment of amoxapine (5-20 mg/kg), clomipramine (0.1325-1.25 mg/kg, p.o.) and fluvoxamine (0.3125-1.25 mg/kg, p.o.) failed to decrease the duration of immobility time in the FS group. In conclusion, these results suggest that the LH group is sensitive to agents with a variety of antidepressant properties compared to the FS group in rats.

The plasma concentrations of amoxapine and its active metabolites, 8-hydroxyamoxapine and 7-hydroxyamoxapine were determined in 8 healthy volunteers receiving a single oral dose of 100 mg of the drug. Considerable interindividual variation was seen in the plasma levels of the three substances. Amoxapine reached maximum levels of 67.4 +/- 35.8 ng/ml between 1 and 2 h after administration. The decline of amoxapine levels in plasma was biphasic. The mean elimination half-life was 9.8 +/- 2.6 h and the estimated first-pass loss ranged between 0.18 and 0.54. The peak levels of the metabolites were reached between 1 and 3 h after administration, with 8-hydroxyamoxapine levels significantly higher than those of 7-hydroxyamoxapine. The mean elimination half-lives were 30.8 and 5.1 h for 8-hydroxyamoxapine and 7-hydroxyamoxapine respectively. The margins of the plasma concentrations reached at steady-state were calculated according to pharmacokinetics parameters for a dosage interval of 8 h.

Loxapine represents an interesting example of old "new" drug and is recently drawing attention for its novel inhalation formulation for the treatment of both psychiatric and non-psychiatric disorders. It is extensively metabolized to several active metabolites with diverging pharmacological properties. To further pursue the contribution of metabolites to the overall outcome after loxapine administration, quantification of both loxapine and its active metabolites is essential. The current study developed a rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of loxapine and its five metabolites (amoxapine, 7-hydroxy-loxapine, 8-hydroxy-loxapine, 7-hydroxy-amoxapine and 8-hydroxy-amoxapine) in rat brain tissues, plasma and cerebrospinal fluid (CSF). By evaluating the effects of perchloric acid and methanol on analyte recovery, the extraction methods were optimized and only small amounts of sample (100 μl for plasma and less than 100mg for brain tissue) were required. The lower limits of quantification (LLOQs) in brain tissue were 3 ng/g for loxapine and amoxapine and 5 ng/g for the four hydroxylated metabolites of loxapine. The LLOQs were 1 ng/ml for loxapine and amoxapine and 2 ng/ml for the four hydroxylated metabolites in plasma, and 10 ng/ml for all analytes in CSF. The developed method was applied to a pharmacokinetic study on rats treated with a low-dose loxapine by oral administration. Four hours after loxapine dosing, high levels of 7-hydroxy-loxapine were found throughout the ten brain regions examined (68-124 ng/g), while only trace amount of loxapine was measured in brain (<5 ng/g) and plasma (<3 ng/ml). The method provides a useful tool for both preclinical and clinical investigations on the dispositions of loxapine and its metabolites, which would help to elucidate their roles in neurotherapeutics.

Loxapine is a dibenzoxazepine tricyclic compound used to treat schizophrenia in the United States since 1976. Metabolism includes demethylation to its primary metabolite, amoxapine. There are few documented reports of the disposition of loxapine in deaths due to overdose. This report discusses the overdose suicide of a 69-year-old white female found dead in her home by her husband. A prescription for loxapine (50-mg capsules) was found near the body. An autopsy was performed and heart blood, bile, vitreous humor, and gastric contents were submitted for toxicological analysis. The blood specimen was subjected to comprehensive testing that included volatile analysis by headspace gas chromatography (GC); acidic/neutral and basic drug screening by GC; benzodiazepine screening by high-performance liquid chromatography; opiate screening by modified immunoassay; and acetaminophen, salicylate, and ethchlorvynol screening by colorimetry. Loxapine and amoxapine were detected in the basic drug screen. No other drugs were detected in the case specimens. The respective concentrations of loxapine and amoxapine in each specimen were as follows: heart blood, 9.5 and 0.6 mg/L; bile, 28.8 and 4.7 mg/L; gastric, 278 mg/L and negative; and vitreous, 1.5 mg/L and negative. A review of the literature showed that the heart blood concentration of loxapine measured in this case was the highest reported to date. Based on the autopsy findings, patient history, and toxicology results, the cause of death was determined to be acute intoxication of loxapine and the manner, suicide.

The effect of traditional tricyclic antidepressants on serum prolactin levels is controversial. In a five-week double-blind study of depressed outpatients, imipramine hydrochloride therapy did not lead to any significant change in serum prolactin levels. In contrast, amoxapine, a new antidepressant, produced significant elevations in serum prolactin levels in female and in male patients. Amoxapine may block dopamine receptors in central tuberoinfundibular pathways, which would account for its prolactin-elevating activity. On the other hand, imipramine and other traditional tricyclic antidepressants do not affect dopamine transmission, do not raise serum prolactin levels, and are not effective antipsychotic drugs.

BACKGROUND

All currently available atypical antipsychotics have, at clinically relevant doses: i) high serotonin (5-HT)2 occupancy; ii) greater 5-HT2 than dopamine (D)2 occupancy; and iii) a higher incidence of extrapyramidal side effects when their D2 occupancy exceeds 80%. A review of pharmacologic and behavioral data suggested that amoxapine should also conform to this profile; therefore, we undertook a positron-emission tomography (PET) study of its 5-HT2 and D2 occupancy.

METHODS

Seven healthy volunteers received 50-250 mg/day of amoxapine for 5 days and then had [11C]-raclopride and [18F]-setoperone PET scans.

RESULTS

5-HT2 receptors showed near saturation at doses of 100 mg/day and above. The D2 receptor occupancies showed a dose-dependent increase, never exceeding 80%; at all doses 5-HT2 occupancy exceeded D2 occupancy.

CONCLUSIONS

PET data show that amoxapine's profile is very similar to that of the established atypical antipsychotics. These data, together with amoxapine's in vitro pharmacologic profile, effectiveness in animal models, and efficacy in psychotic depression raise the possibility of amoxapine as an "atypical" antipsychotic agent in the treatment of schizophrenia.

A total of 61 moderately to severely depressed outpatients were treated for four weeks with either amoxapine (a dibenzoxapine tricyclic) or amitriptyline. This double blind study showed that amoxapine was as effective as amitriptyline and had an earlier onset of action. Maximum doses used were 300 mg of amoxapine and 150 mg of amitriptyline. Side effects were similar for the two drugs, except for impotence or loss of libido in eight male amoxapine, as against three amitriptyline patients. Laboratory, EKG, and vital signs findings showed no pathological trends.

The authors provide a literature review and assess amoxapine's clinical pharmacology, therapeutic efficacy and side effects. They conclude that Amoxapine is indicated for use in moderate to severe depressions, has a favorable side effect profile and probably has an earlier onset of action than other tricyclic antidepressants.

Overdose of tricyclic antidepressants remains one of the most difficult poisonings to manage optimally in the emergency department, primarily due to the extremely rapid onset of life-threatening symptomatology. The continued high incidence of such overdoses has ensured that morbidity and mortality rates also remain unacceptably high. The development of the "second-generation antidepressants," with apparently different pharmacology and toxicity after overdose, has been an attempt to address this serious medical problem. This report reviews the published literature on the overdose toxicology of the newer cyclic antidepressants currently available in the United States--amoxapine, maprotiline, and trazodone. Nomifensine, released by the FDA in 1984, recently has been voluntarily withdrawn from the world market. Bupropion, released in 1985, also has been voluntarily withdrawn by the manufacturer three months after its release.

A young woman developed galactorrhea during treatment with a new dibenzoxazepine antidepressant, amoxapine. Both amoxapine and its active and major metabolite, 8-OH-amoxapine, appeared in breast milk. More recent literature suggests that probably all antidepressants can appear in human milk.

2-Chloro-11-(piperazinyl)dibenz[b,f][1,4]-oxazepine (amoxapine) gives an unusual spectrum in psychopharmacological tests. Many of its effects are similar to those of neuroleptics: sedation, decrease in motor activity, catalepsy (which is, however, qualitatively different from that induced by classical neuroleptics), transitory suppression of avoidance reaction, antagonism of amphetamine induced toxicity in crowded mice and inhibition of stereotyped behavior induced by amphetamine in rats, and antagonism to various effects of apomorphine (stereotyped behaviour in rats, climbing behaviour, stereotyped behaviour and hypothermia in mice). At similar doses which produce the above mentioned effects, amoxapine also shows effects atypical for a neuroleptic, but which are relatively characteristic of antidepressants: antagonism of prochlorperazine-induced catalepsy in rats, inhibition of reserpine induced hypothermia in mice and enhancement of yohimbine toxicity in mice. The profile of this substance does not facilitate the anticipation of therapeutic effects in humans.

Antidepressant drugs, such as the tricyclics and the serotonin reuptake inhibitors, are well known to decrease paradoxical sleep and occasionally increase slow wave sleep in human and in animals. In order to examine whether amoxapine (a mixed NA reuptake blocker and 5-HT2/5-HT3 antagonist) and cericlamine (a selective 5-HT reuptake inhibitor) exert the same effect in rats, and to investigate the possible relationships between sleep, the action of antidepressants and the serotoninergic system, the effects of these two different drugs were examined under acute and chronic conditions. Acutely, amoxapine (1, 5 and 10 mg/kg; i.p.) and cericlamine (1, 8, 16 and 32 mg/kg; i.p.) decreased paradoxical sleep and increased deep slow wave sleep especially when they were given at a low dose. When administered for 14 days, amoxapine induced a sustained decrease of paradoxical sleep during the whole treatment, while some tolerance was observed with regard to the inhibitory effect of cericlamine on this state of sleep. In addition, a rebound of paradoxical sleep occurred on the first day of cericlamine withdrawal. Thus, amoxapine and cericlamine exerted the same effects on the states of vigilance in the rat as do other antidepressants. The effects of cericlamine on sleep probably reflect its blocking action on 5-HT uptake, whereas the more complex effects of amoxapine might involve its 5-HT2/5-HT3 antagonist properties.

BACKGROUND

The dibenzoxazepine amoxapine was introduced as an antidepressant but has shown antipsychoticlike activity in a number of animal screening tests. A recent positron emission tomography study showed a 5-HT(2)/D(2) receptor occupancy profile of amoxapine that is very similar to that of established atypical antipsychotics. Schizophrenics display deficits in sensory gating mechanisms, such as prepulse inhibition (PPI) of the acoustic startle reflex. A similar deficit can be produced by dopamine (DA) and by 5-HT(2A/C) receptor agonists in rats. Antipsychotic compounds reverse this effect.

METHODS

Effects of amoxapine on apomorphine- or 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced disruption of PPI were studied in adult male Sprague-Dawley rats. The extrapyramidal side effect (EPS) liability of amoxapine was assessed using the inclined grid catalepsy (CAT) test. Statistical analyses were performed by analysis of variance (ANOVA) for fully repeated measures (PPI) and by the Kruskal-Wallis one-way ANOVA by ranks (CAT).

RESULTS

Apomorphine (0.5 mg/kg) produced a significant reduction in PPI compared with the case of rats in the saline control group. Pretreatment with amoxapine (10 mg/kg) significantly attenuated the apomorphine-induced disruption of PPI. DOI (0.5 mg/kg) significantly reduced PPI compared with saline controls. Pretreatment with amoxapine (5 or 10 mg/kg) produced a significant attenuation of the DOI-induced disruption of PPI. Amoxapine by itself did not alter PPI. Amoxapine (5 or 10 mg/kg) did not produce CAT.

CONCLUSIONS

The DA D(2)/5-HT(2) receptor antagonist amoxapine produced an antipsychoticlike reversal of both apomorphine- and DOI-induced disruption of PPI. Furthermore, the same doses of amoxapine that reversed disruption of PPI did not produce CAT. The results confirm and lend further support to the results of previous studies on amoxapine, suggesting that amoxapine might possess antipsychotic activity with little propensity for producing EPS.